Many porous solids have the ability to interact with atoms, ions and molecules not only at their surfaces, but throughout the bulk of the material. In addition, porous solids can serve as hosts for guest species. These features of porous solids can be used in a wide variety of applications, including chemical processes and electronic applications. Some of the chemical process areas in which porous solids are useful include fluid separation, catalytic reactions, adsorption of ions or molecules, purification of compounds, and the like. The ability of porous solids to serve as hosts for guest species can be used to impart the material with optical, electrical or magnetic properties by selecting appropriate guest species, thereby making porous solids useful in a variety of optical and electronic applications.
Typically, porous solids are classified according to the average pore diameter. For example, microporous solids have an average pore diameter, i.e., pore size, of about 2 nm or less, mesoporous solids have an average pore size in the range of about 2 nm to about 50 nm, and macroporous solids have an average pore size of about 50 nm or greater. See “Ordered Porous Materials for Emerging Applications”, Davis, Nature, 2002, 417, 813-821, and references cited therein, all of which are incorporated herein by reference in their entirety.
Synthetic porous solids are generally produced by adding an organic compound (i.e., template or structure directing agent or SDA) to an inorganic material precursor solution, precipitating the inorganic material from the solution to form a nano-composite material in which the organic compound is intimately and/or uniformly dispersed within a solid inorganic material structure, and removing the organic compound from the solid inorganic material structure, i.e., nano-composite material. The organic compound serves as a template for pores, and the pore size of the solid inorganic material depends on the size of the organic compound that is encapsulated or entrapped within the framework of inorganic material. When an organic surfactant is used as a template, the pore size of the solid inorganic material is relatively large because the framework of inorganic material is built around the micelles, i.e., colloidal particles, formed by the surfactant. Micelles are inherently larger in size than their constituents. Thus, using a surfactant as a template generally produces mesoporous solids.
As stated above, pores are produced in the inorganic material framework by removing the encapsulated organic compound from the nano-composite material. Often, thermal methods, i.e., calcination processes, are used to remove the organic compound from the nano-composite material. Calcination of the nano-composite material typically involves heating the nano-composite material under a flow of oxygen or air to about 500° C. or higher and maintaining the heating temperature for several hours. Thus, a large amount of energy is expended in the calcination process leading to a relatively high cost of producing such porous solids.
Additionally, some nano-composite materials are not thermally stable, and calcination processes can not be used to remove the organic compound. While other methods, such as solvent, plasma and supercritical fluid extraction, have also been used to remove the organic compound from the nano-composite material, each has its own disadvantages and limitations. For example, waste disposal of hazardous solvents can be quite expensive and the high reactivity of plasma may result in destruction of some of the inorganic materials.
Recently, ozone treatment to remove surfactants from silicate and aluminosilicate materials to produce MCM-type mesostructure has been reported. See Keene et al., Chem. Commun., 1998, 2203-4, and Büchel, et al., J. Mater. Chem., 2001, 11, 589-593. Materials that are produced in these ozone treated mesostructures reportedly have a larger pore size compared to calcined MCM-41 mesostructures. Moreover, the authors report that ozone treatment to produce “microporous materials such as zeolites, could be hampered by the steric hindrance of the micropores themselves.” Keene et al., Chem. Commun., 1998, at 2203.